Bone fixation system

ABSTRACT

A cerclage fixation component and a screw fixation component are engageable together to form a composite bone fixation device. The cerclage component may be a ladder plate with openings defined between bridges. The openings provide sockets for bosses of the screw fixation component.

This application is filed under 35 U.S.C. 371 based on PCT/GB93/00566which was filed on Mar. 19, 1993.

TECHNICAL FIELD

The present invention relates to a bone fixation system, andparticularly (though not exclusively) to a system that may be employedin bone implant surgery such as hip replacement operations, orsubsequent surgical treatment of the bone structure in the region of animplant. The term `bone fixation` is intended to cover not only theconnection of bone to bone but also the connection of components tobone.

BACKGROUND ART

Cerclage is a known fixation technique in which a bone is encircled by aflexible member such as a cable which is drawn tight and clamped. Thismay serve to hold portions of bone or bone graft together and/or toretain some surgically applied component. For an account of currentcable techniques for trochanteric reattachment, femoral allograftfixation and fractures of the proximal femur in revision total hiparthroplasty, the reader is referred to D. M. Dall, Techniques inOrthop. 1991; 6(3):7-16. This describes, among other things, use of abone fastener for the greater trochanter, as disclosed in U.S. Pat. No.4,269,180. This known bone fastener is a generally H-shaped implantcomprising a base structure including a pair of limbs joined by abridge, the bridge being bounded by a front face, a rear face and edgefaces, a plurality of teeth protruding from the base structure, all theteeth lying on the same side of the base structure, and at least onehole in the base structure for receiving a cable, the hole beingelongate in form, extending lengthways through the bridge, and beingopen at each end. The bridge is adapted to be crimped so that cable(s)can be passed through the hole(s), pulled tight, and then locked bycrimping.

FIG. 1 is a drawing, taken from the cited paper, showing a femur 10 thathas undergone reconstructive surgery including use of a fastener 12according to U.S. Pat. No. 4,269,180. In this procedure, the greatertrochanter 16 was cut (osteotomised) to facilitate installation in thebone cavity of an internal bone graft 14 and the stem of a prosthesis(not shown but corresponding to stem 71 in FIG. 7). Thereafter thegreater trochanter 16 was reattached to the femur 10 by means of thefastener 12 and cerclage cables 18. In addition a fracture 20 of thefemur was surgically treated with a further application of cerclagetechniques. Thus elongate medial and lateral bone grafts 22 have beenapplied to the bone, and bound in place by a multiplicity of cerclagecables 25, each of which has been drawn tight and had its ends locked bycrimping in an individual crimp sleeve 26.

A disadvantage of cerclage fixation is that it tends to providerelatively little resistance to some forms of displacement, e.g.relative rotation of components and/or portions of bone and/or bonegrafts encircled by cerclage cables. Furthermore some shapes andlocations are not well suited to cerclage. A second technique involvesscrews, which are screwed into bone. A screwed connection is commonlyquite good at resisting relative displacement such as rotation. Butparticularly where the bone is weak, e.g. being spongy, a screwedconnection will be of low mechanical strength. Furthermore, if screwingwere to be substituted for cerclage for securing the bone grafts 22shown in FIG. 1, there would be a problem in the upper region, in thatonly short screws could be used since otherwise they would meet the stemwhich is typically of metal. Thus cerclage and screw fixation each haveadvantages and disadvantages, and it would be desirable to have a systemthat made the advantages of both available.

DISCLOSURE OF INVENTION

According to the present invention there is provided a bone fixationsystem comprising first and second fixation means each having at leastone fixation element receiving means, wherein said first fixation meanscomprises a cerclage fixation means, having a body which defines atleast one passage for a cerclage cable and has deformable portions whichare deformable to crimp a cerclage cable in said passage, said passageconstituting a said fixation element receiving means; and said secondfixation means comprises a screw fixation means having at least onescrew receiving opening constituting a said fixation element receivingmeans; said first and second fixation means having complementary mutualengagement formations so that they can be located together to form acomposite fixation means capable of fixation by means of both at leastone cerclage cable and at least one screw.

Preferably at least one of the first and second fixation means iselongate and has a plurality of fixation element securement means.Preferably an elongate fixation means has a plurality of engagementformations along its length, so that a complementary engagementformation of another fixation means is selectively engageable at plurallocations.

In one preferred type of embodiment, the cerclage fixation meanscomprises a ladder body comprising a pair of elongate side limbs bridgedby a plurality of longitudinally spaced bridges. The bridges may providethe cerclage cable passages and deformable crimping portions. There areopenings defined between adjacent bridges, and portions of the sidelimbs, and the limb portions are shaped to provide complementaryengagement formations for screw fixation means. Thus a screw fixationmeans may comprise a shaped, e.g. tapered, boss, and the side limbportions of the ladder body may provide a complementarily shaped recess.

In another aspect the invention provides a kit of parts comprising amultiplicity of first and second fixation means, whereby a range ofcomposite fixation means can be provided.

In a third aspect the invention provides a cerclage fixation means(which may be usable in a composite fixation means as defined above),comprising an elongate ladder member having respective elongate sideportions at both lateral sides, and a multiplicity of bridge portionsconnecting side portions, adjacent bridge portions being spaced so as todefine openings; there being through-holes for cerclage cables extendingacross the ladder member through at least some of the bridge portions.Such a ladder member may have means for receiving fixing screws. Thesemay be apertured portions for receiving screws directly and/orformations (e.g. sockets) in which screw receiving means are engageable.

In a fourth aspect the invention provides a method of connecting orsupporting an article or assembly (preferably comprising a bone) whichcomprises connecting thereto a fixation means provided by the inventionaccording to the first, second or third aspect.

Some embodiments of the present invention will now be described in moredetail by way of example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a bone structure with bone fixationelements of the prior art;

FIG. 2 is a perspective view of a fractured bone with fixation elementsaccording to a first embodiment of the present invention;

FIG. 3 is a perspective view on a larger scale of a part of a ladderplate of the first embodiment;

FIG. 4 is a perspective view of a single-screw fixation means of thefirst embodiment;

FIG. 5 is a section on V--V in FIG. 2;

FIG. 6 is a perspective view from beneath of a part of a many-screwfixation means of the first embodiment;

FIG. 7 shows a practical application of the first embodiment in treatinga femur which has a fracture at the tip of the prosthetic stem;

FIG. 8 is a perspective view showing another practical application totreat a complex fracture with a butterfly fragment;

FIGS. 9 and 10 are front and side views of a bone structure with avariant of the first embodiment;

FIG. 11 shows a bone structure with a further variant of the firstembodiment;

FIG. 12 is a side elevation of a bone structure with fixation elementsaccording to a second embodiment of the invention;

FIG. 13 is a side elevation on a larger scale showing portions of thefixation means of the second embodiment;

FIG. 14 is a side elevation on a still larger scale showing a variant ofthe embodiment shown in FIG. 13; and FIGS. 15 and 16 are like views offurther variants;

FIG. 17a is a top plan view of a ladder plate with screw holes, and FIG.17b is a section on y--y;

FIG. 18 is a perspective view of another form of elongate fixationmeans;

FIG. 19 is a sectional view through an elongate fixation means as shownin FIG. 18 and further showing a sleeve element engaged in a slot;

FIG. 20 is a view like that of FIG. 2 showing another embodiment;

FIG. 21 shows details of the components of the FIG. 20 embodimentseparated;

FIG. 22 is a view like that of FIG. 21 but showing a variant;

FIG. 23 is a section of a ladder plate e.g. as shown in FIG. 3, onXXIII--XXIII;

FIG. 24 is a view similar to that of FIG. 23 showing a modification;

FIG. 25 shows a detail of modified cerclage fixation component; and

FIG. 26 shows a detail of modified screw fixation component; and

FIG. 27 is a view like that of FIG. 21 but showing a further embodiment.

MODES FOR CARRYING OUT THE INVENTION

FIG. 2 shows a bone 30 having a fracture 32. The bone is held togetherby a composite fixation means 34 comprising a ladder plate 36, asingle-screw fixation means 38, and a many-screw fixation means 40. Theladder plate 36 is a unitary body having the form of a pair of sidelimbs 39 connected by bridges 42 (FIG. 3). Thus there are defined aplurality of openings 44, each approximately rectangular in plan. Theunderside 46' of the plate 36 is curved to conform to the surface of thebone 30 to which it is to be applied. Pairs of holes 48 pass through theplate 36 in the region of each bridge 42. (A variant could have singleholes.)

Each opening 44 is delimited by an edge 46 that generally extends atright angles to the upper surface 49 of the plate. However, atintermediate regions of the longitudinal portions, there are taperportions 50 which together define an engagement formation delimiting asocket in the opening 44, spaced from the adjacent bridges 42. FIG. 4shows a single-screw fixation means 38. FIG. 5 shows such a fixationmeans 38 located in one of the sockets of the ladder plate. The fixationmeans 28 has a body with a pair of opposed faces 54 that have acomplementary taper to the taper portions 50 in the ladder plate 36. Thebody also has a hole 56 to accommodate the shaft of a screw 58, and acounter-sunk portion 59 to accommodate the head. (In generally knownfashion, the hole and counter-sinking may be relatively large so that ascrew can be angled so that its angle of penetration into the bone canbe adapted to particular circumstances.) Whereas the width of thefixation means between the tapered faces 54 substantially corresponds tothe width of the opening 44, in the longitudinal direction the fixationmeans is substantially narrower than the opening 44 (in this examplebeing no wider than the longitudinal extent of the taper portions 50).Thus even when the single screw fixation means 38, is located in anopening 44, it is still possible to crimp an adjacent bridge 42 with acrimping tool. Furthermore, distortion of a bridge caused by crimpingdoes not interfere with subsequent location of a (single or many-screw)fixation means.

FIG. 2 also shows a many-screw fixation means 40, whose underside isshown in FIG. 6. It can be seen that it has the form of an elongateplate 60 whose underside has a plurality of bosses 62 each of which hasa form substantially corresponding to that of a single-screw fixationmeans 38. Of course, the spacing of these bosses 62 corresponds to thespacing of the openings 44 in the ladder-plate 36. Thus, as shown inFIG. 2, the many-screw fixation means 40 can be located at a requiredposition along the length of the ladder plate 36.

For practical use, the ladder plate 36 may first be mounted on the bone30 and secured there by cerclage, the cerclage cables 64 being passedthrough holes 48. Each loop of cable is pulled tight and then locked inplace by crimping a respective bridge 42, in a generally conventionalway. Thereafter one or more single-screw and/or many-screw fixationmeans can be coupled to the ladder plate, and fixed to the bone 30 bymeans of screws 58. Note that the complementary engagement formationsare spaced from the bridges 42, so that the deformation of the bridgesassociated with the crimping of the cables 64 does not affect the properseating.

FIG. 7 shows a composite fixation means 34a generally as previouslydescribed, applied to a situation similar to that shown in FIG. 1,namely to a femur which has received an implant 70 and subsequentlysustained a fracture 72. Thus there is a ladder plate 36a which extendson both sides of the fracture 72 and is secured to the bone 30 bycerclage cable 74. In this particular example, the ladder plate 36a hassix openings. The lower three of these are covered by a three-screwfixation means 76, while the upper three contain single-screw fixationmeans 38 (not shown). These are secured to the bone by means ofunicortical screws 78; that is, by relatively short screws that extendonly a short way into the central cavity. Thus their use is notprevented by the presence of the shank of the implant 70. Below theimplant 70, use is made of bicortical screws 80, which extenddiametrally across the bone and engage both cortices.

FIG. 8 shows a seven-opening ladder plate 81 and a five-opening ladderplate 82 used for bracing a complex fracture 83 with a butterflyfragment 84. The end openings of at least the upper ladder plate 81contain single-screw fixation means 38, which are screwed to the bone.

FIGS. 9 and 10 show a variant in which the many-screw fixation means 90extends beyond a ladder plate 36b. In this example, it is formed as aT-plate insert. Thus, remote from the ladder plate 36b it has across-piece 92 having screw-receiving openings 94. As can be seen fromFIG. 10, it is contoured to embrace the bone, in this case being adaptedfor treatment of a supracondylar fracture.

As shown in FIG. 11, it is also possible to use a contoured ladder plate100 (in this example, in conjunction with two single-screw fixationmeans 38).

FIGS. 12 and 13 show a second type of embodiment differing from thosepreviously described in that the ladder plate 136 is intended to locateover the many-screw fixation means 140, which is located against thebone 30. In the example shown in FIG. 12, the many-screw fixation means140 also has an additional functionality. Thus it projects beyond theladder plate 136 and has a generally conventional formation 200 forengaging a sliding hip-screw 202, for use in fixation of the femoralhead 204 in a subcapital fracture 205.

As can be seen from FIG. 13, the many-screw fixation means 140 isgenerally similar to that shown in FIG. 6, in that it has bosses 162.However, in the intended mode of use, these face away from the bone. Theopposite face 206, which lies against the bone, will generally becontoured to fit it. The ladder plate 136 is generally similar to thatshown in FIG. 3, notably in having bridges 142, cable holes 148 andopenings with taper portions defining sockets 150. But in the intendedconfiguration of use, the sockets enlarge towards the bone, and theopposite face 146 will generally be planar. Particularly when a ladderplate is intended to locate over the screw fixation means, it may bedesirable for the ladder plate (or other cerclage component) also to befixable with screws. Where the two fixation means overlap, they may havescrew openings in register. Thus FIG. 14 shows a variant of FIG. 13 inwhich a ladder plate 136' has at least a portion 36' that resembles theladder plate 36 shown in FIGS. 2 and 3, with holes 48' and openings 44'that can receive screw plate inserts, e.g. single screw plate inserts38. The underlying screw plate 140' has holes in register with thescrew-holes 56 of the inserts 38 when these are in the openings 44'.Thus screws can be used to connect the ladder plate 136' to the screwplate 140', and to secure both of them to an underlying bone. The screwplate 140' need not then have bosses 162. FIG. 15 shows an alternativein which a ladder plate 136" has a portion 36" with openings 44" withdouble socket formations 50", widening towards the top and bottom faces.The underlying screw plate 140" then has small bosses 162" for seatingin the lower portions of the double sockets; and screw plate inserts 38"seat in the upper portions of the sockets 50".

FIG. 16 shows a further variant in which a screw plate insert 238 has alower threaded portion 238a for engaging a complementary thread 239 inthe underlying screw plate 240. This idea of connecting together the twofixation means can be applied to other forms of fixation means, and canbe effected with other forms of connecting element.

FIG. 17 a and b show a variant in which a ladder plate 336 is similar tothe plate 36 as shown in FIG. 2, but has screw holes 357. Such a platemay be used on its own or in conjunction with a screw plate. A plate foruse on its own may have a multiplicity of screw holes 357. It may thenonly have small ladder openings 344' since there would be no need forthe larger, socket-providing openings 344.

FIGS. 18 and 19 show another type of embodiment in which an elementcorresponding to the ladder plate of (e.g.) FIG. 2 is an underlyingscrew plate 340, having alternating countersunk screw holes 356 andslots 390. The slots, which may have tapered or straight walls, receivemating portions 392 of crimp sleeves 394. These have portions 396 thatproject from the slots 390 and have through-holes 398. The projectingportions are deformable to crimp a cable in a hole 398 or pair of holes.

FIG. 20 shows a presently preferred embodiment having an elongatecerclage fixation device in the form of a ladder plate 436 (withcrimpable bridges 442 and socket portions 450). This engages on top ofan elongate screw fixation device 440 which has projecting bosses 462and a lower face 406 which is curved to lie against the surface of abone 30. Each boss has an opening 456 for a screw 58. It may begenerally desirable for screw openings to be staggered, as shown here,so that the screws do not tend to produce a line of weakness in thebone. Other details are similar to those shown in FIGS. 12 and 13. FIG.21 shows portions of the devices 436,440 separated. The screw fixationdevice 440 has a wide base plate 460 which extends laterally beyond theprojections 462. The ladder plate 436 is a flat plate of the same width.FIG. 22 shows a variant in which the screw fixation device 540 isrelatively narrower, the base plate 560 in the example being of the samewidth as the projections 562. The cerclage fixation device 536 ischannel shaped, so that it locates over and substantially conceals thescrew fixation device.

FIG. 27 shows that a ladder plate 636a need not have continuous sideportions. It can have staggered short portions 639a connected by bridges642a. The resulting zigzag plate 636 can embrace bosses 662 on anelongate screw fixation plate 660. The bosses 662 are laterallystaggered. Thus the screw openings 656 can also be staggered as isdesirable.

Hitherto it has been assumed that holes for cerclage cables are simpleuniform bores 400 as shown in FIG. 23. However it may be preferable fora bore to follow an arcuate path, e.g. in parallel with a curved rearsurface 406. Alternatively or additionally a bore may have shaped mouths404 as shown in FIG. 24, to provide a smoother cable path around thebore.

FIG. 25 shows a detail of a cerclage fixing device 636b to illustrate avariant form of crimping bridge. The device 636 has side portions 639bconnected by bridges 642b. The bridges 642b have portions of reducedwidth adjacent the side portions 639b (shown here as due to opposedpairs of scallops 690). This is to facilitate crimping and reduce therisk of cracks at the bridge/side portion junction.

FIG. 26 shows a modified screw plate insert 638. This comprisesdeformable material to assist seating in a socket of a cerclage fixationdevice, to reduce fretting, and to allow for deformation when anassembly is secured to a bone.

In this example there is a metal insert 696 in which the screw-hole 656is defined; and this is set in a plastics liner 698. Of courseprojecting bosses of long screw-plates (e.g. as shown in FIG. 6) couldsimilarly be formed with plastics liners.

For surgical use, the components must all be made of biocompatiblematerials. Generally the ladder plates and screw fixation means will beof metal, for example stainless steel, chrome cobalt, or titanium alloy,optionally with liners (as described with reference to FIG. 26) ofbiocompatible deformable plastics materials. All metal components of asingle system (which may include the cable) should be of the samematerial, or materials which are compatible, to avoid electrolyticeffects.

The component which is intended to locate against the bone may haveformations to assist gripping to the bone surface, such as serrations or"teeth".

Fixation systems embodying the present invention may be used in humanand veterinary surgery. Of course, the same principles will also beapplied to connection of elements in other fields.

We claim:
 1. A bone fixation system comprising:cerclage cables; and anelongate unitary body including a top face, a bottom face, a spaced pairof elongate side portions which define an oppositely directed pair oflateral edges, a multiplicity of spaced-apart bridge portions connectingsaid side portions, said bridge portions each having a pair ofoppositely directed side edges shaped so that a plurality ofapproximately rectangular openings are defined between opposed sideedges of adjacent bridge portions, and pairs of through-bores forreceiving said cerclage cables disposed therein; wherein said pairs ofthrough-bores are located between adjacent approximately rectangularopenings and extend through said bridge portions, each of said pairs ofthrough-bores being positioned within said bridge portions such thatcrimping said side edges of each of said bridge portion substantiallycloses said pair through-bores to secure said cerclage cable disposedtherein; wherein said elongate unitary body is adapted to be locatedwith said bottom face overlying a bone and fixed thereto by passing saidcerclage cable around the bone and through one of said pairs ofthrough-bores, pulling the cable tight, and locking it in place bycrimping the bridge through which said through-bores pass.
 2. A bonefixation system as in claim 1 further comprising a screw fixation meansfor bridging broken bones which is affixed to bone by at least one screwhaving at least one screw receiving opening; said cerclage receivingmeans and said screw fixation means having complementary mutualengagement formations so that they can be located together to form acomposite fixation means capable of fixation by means of both at leastone cerclage cable and at least one screw.
 3. A bone fixation systemaccording to claim 2 wherein said screw fixation means is elongate andhas a plurality of said screw receiving openings.
 4. A bone fixationsystem according to claim 3 wherein at least one of said cerclagereceiving means and screw fixation means is elongate and has a pluralityof engagement formations along its length, so that a complementaryengagement formation of another fixation means is selectively engageableat plural locations.
 5. A bone fixation system according to claim 2wherein said side portions of the elongate ladder member are shaped toprovide complementary engagement formations for said screw fixationmeans in said openings.
 6. A bone fixation system according to claim 5wherein said screw fixation means comprises a shaped boss, and said sideportions of the elongate ladder member provide a complementarily shapedrecess.
 7. A bone fixation system according to claim 6 wherein the bossand recess are dimensioned so that the recess and the boss when engagedtherein are spaced from the adjacent bridge portions.
 8. A bone fixationsystem according to claim 6 wherein the screw fixation means is elongatewith a plurality of screw-receiving bosses along its length.
 9. A bonefixation system according to claim 2 wherein the screw fixation means iselongate, having a first portion for engaging the cerclage fixing meansand a second portion for extending beyond the cerclage receiving meansand being adapted for connection to bone or to a bone implant.
 10. Abone fixation system according to claim 2 wherein the cerclage receivingmeans has a first major face which is contoured for lying against bone,and an oppositely-facing second major face at which the screw fixationmeans is applied to engage the engagement formations.
 11. A bonefixation system according to claim 2 wherein the screw fixation meanshas a first major face which is contoured for lying against bone, and anoppositely-facing second major face at which the cerclage receivingmeans is applied to engage the engagement formations.
 12. A bonefixation system according to claim 2 wherein the cerclage receivingmeans also has means for screw fixation.
 13. A bone fixation systemaccording to claim 2, wherein said first screw fixation means iselongate with a plurality of engagement means; at least one second screwfixation means comprising at least one shaped boss; and a cerclagereceiving means which is elongate and has a plurality of throughopenings extending from a first major face at which they are engageablewith respective engagement means of the first screw fixation means, to asecond major face at which they are shaped to engage a boss of thesecond screw fixation means.
 14. A bone fixation system according toclaim 13 wherein the engagement means of the first screw fixation meanscomprise upstanding bosses.
 15. A bone fixation system according toclaim 13 or claim 14 wherein the second screw fixation means and theengagement means of the first screw fixation means have mutualengagement formations, and the through-openings of the cerclagereceiving means are adapted to allow their mutual engagementtherethrough to connect said first and second screw fixation means andsaid cerclage receiving means together.
 16. A kit of parts for use inproviding a bone fixation system according to claim 2 comprising firstand second fixation means, at least some of which are elongate and havea multiplicity of engagement formations, there being a plurality ofdifferent first fixation means and/or a plurality of different secondfixation means.
 17. A bone fixation system according to claim 1 whereinthe ladder member has means for receiving fixing screws.
 18. A bonefixation system as claimed in claim 1, wherein said openings are locatedon said top face and said through-holes are located on said lateraledge, said top face being substantially perpendicular to said lateraledge.
 19. A bone fixation system as claimed in claim 1 wherein saidbottom face is curved to conform to the surface of the bone to whichsaid system is applied.
 20. A method of bone fixation comprising thesteps of:providing cerclage cable and an elongate unitary body having atop face, a bottom face and a spaced pair of elongate side portionswhich define an oppositely directed pair of lateral edges, amultiplicity of spaced-apart bridge portions connecting said sideportions, said bridge portions each having a pair of oppositely directedside edges shaped so that approximately rectangular openings are definedbetween opposed side edges of adjacent bridge portions, pairs ofthrough-bores for cerclage cables, wherein said pairs of through-boresextend through said bridge portions, each of said bridge portions beingadapted to be crimped by a crimping tool which engages said pair ofoppositely directed side edges thereof; locating said elongate unitarybody so that said bottom face overlies a bone requiring fixation;passing a length of cerclage cable around the bone and through a saidpair of through-bores; pulling the cable tight; and locking the cable inplace by crimping the bridge through which said bores pass.
 21. A bonefixation system comprising:cerclage cables; an elongate unitary bodyincluding a top face, a bottom face, a spaced pair of elongate sideportions which define an oppositely directed pair of lateral edges, amultiplicity of spaced-apart bridge portions connecting said sideportions, said bridge portions each having a pair of oppositely directedside edges shaped so that approximately rectangular openings are definedbetween opposed side edges of adjacent bridge portions, and pairs ofthrough-bores for said cerclage cables; wherein said pairs ofthrough-bores extend through said bridge portions, each of said bridgeportions being adapted to be crimped by a crimping tool which engagessaid pair of oppositely directed side edges thereof; wherein saidelongate unitary body is adapted to be located with said bottom faceoverlying a bone and fixed thereto by passing cerclage cable around thebone and through one of said pairs of through-bores, pulling the cabletight, and locking it in place by crimping the bridge through which saidthrough-bores pass; screw fixation means positioned in saidapproximately rectangular opening for affixing said elongate unitarybody to the bone, wherein said screw fixation means, once fixed, stillallows said crimping tool to crimp said bridge portion and lock saidcerclage cables.